Self-Assembly of Pentameric Porphyrin Light-Harvesting Antennae Complexes

Abstract

The reaction centers of natural photosynthetic systems are excited indirectly through their light-harvesting antennae complexes. [1±3] These units contain a network of chromophores which absorb light energy and channel this very efficiently by singlet energy transfer to the photochemical reaction centres. [4, 5] The photochemical properties of porphyrins lend themselves to the design of artificial organic antennae systems, [6] and covalently linked arrays of five or more porphyrins have been constructed. [7±10] We demonstrate here that cooperative self-assembly processes are ideally suited to the construction of stable structurally well-defined chromophore arrays for use as antennae systems. [11, 12] Zn 2 1 and H 2 2 were designed to be perfectly complementary, preorganized partners for the self-assembly process shown in Scheme 1. [13] Intramolecular hydrogen bonds constrain both molecules to essentially one conformation, thus minimizing the loss of rotational entropy upon binding. The spacing of the coordination sites ensures that Zn 2 1 will coordinate to the trans-meso ligands across the face of H 2 2 with no strain in the final complex. [14] The central free-base porphyrin is encapsulated in a spherical array of four zinc X-ray diffraction: Tube measurements were done at room temperature on a Bruker SMART CCD diffractometer (Mo Ka ). Data collection and integration was carried out with the SMART software. Averaging and empirical absorption corrections were carried out with SADABS. [10] Least-squares refinements were made with programs LINEX [11] and XD [12] in the space group Pm3 Å n. For both structures free refinement of framework atom occupancies resulted in random distributions of Ga and Ge atoms. Refinement of guest atoms occupancies showed all sites to be fully occupied except Sr(1), which refined to 98.6(4) % occupancy. In both refinements anisotropic thermal parameters were employed on all atoms as well as isotropic extinction parameters. For Sr 8 Ga 16 Ge 30 a split-atom model was used for Sr (2) as in reference [6] ((x, y, z) (0, 0.4784, 0.9784)). Sr 8 Ga 16 Ge 30 [Ba 8 Ga 16 Ge 30 ]: a 10.740(2) [10.785(2)] , V 1238.7(1) [1254.4(1)] 3 , V crystal 0.0004 [0.0003] mm 3 , 1 calcd 5.354 [5.791] g cm À3 , l 0.7107 , (sinq/l) max 0.923 [0.836] À1 , m l 345 [322] cm À1 , T max , T min 0.2060, 0.0883 [0.2534, 0.1132], no. of measured reflections 35 927 [54 576], no. of unique 691 [558], R w (int) 0.0451 [0.0361], N obs 691 [558] (I > 0s(I)), N par 19 [16], GOF 0.40 [0.52], R F 2 0.0256 [0.0170], R wF 2 0.0254 [0.0169], Y min (extinction) 0.79 [0.81] (10 and 8 reflections have Y < 0.95). Further details on the crystal structure investigations may be obtained from the Fachinformationszentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany (fax: ( 49) 7247-808-666, on quoting the depository numbers CSD-411062 (Sr 8 Ga 16 Ge 30 ) and CSD-411063 (Ba 8 Ga 16 Ge 30 )).MEM calculations: Absorption, extinction, and anomalous dispersioncorrected observed structure factors phased and scaled with program X...

Investigation of Morphology‐Controlled Ultrafast Relaxation Processes of Aggregated Porphyrin

“…Porphyrin based supramolecular self-assemblies have been considered as emerging nanomaterials for optoelectronics, catalysis, light energy conversion and sensing applications. [1][2][3][4][5][6][7][8][9] Morphology of self-assemblies is governed by the intermolecular π-π electronic coupling which controls the properties of the aggregates. [10][11][12] Aggregation stimulates the extent of coherent electronic delocalization through the strong intermolecular π-π electronic coupling among the cooperatively aligned chromophoric units and the properties of aggregates may also differ with size as well as shape of the aggregated moieties.…”

Unusual Photoinduced Electron Transfer from a Zinc Porphyrin to a Tetrapyridyl Free‐Base Porphyrin in a Noncovalent Multiporphyrin Array

“…[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Multiple binding sites and a nearly perfect geometrical matching between partners has been a successful strategy to synthesize associates with very-high stability. [24][25][26][27] This is a prerequisite for a photophysical investigation, which generally involves determination at very-low spectroscopic concentrations.…”

Supramolecular polymer formed by reversible self-assembly of tetrakisporphyrin

“…Hunter and coworkers developed unique self-assembled porphyrin arrays (14)(15)(16)(17)(18). Giant porphyrin arrays and large porphyrin wheels via metal coordination for modeling light-harvesting antenna have been reported by .…”